Torsion keys allow adjustment to increase or decrease the load on the torsion bars in a car, thereby raising or lowering the vehicle and making the suspension much stiffer or softer. A vehicle's torsion bar suspension uses a straight torsion bar instead of a coil or leaf spring for the suspension travel and control. The torsion bar typically attaches to the front suspension and attaches to the chassis by torsion keys. The torsion keys attach at a 90-degree angle to the torsion bar and use mounted adjusting bolts to operate the vehicle's suspension.
The typical torsion bar is octagonal where it connects to the torsion keys. By indexing the torsion keys on the torsion bar, the amount of lift can be altered. In applications such as off-road trucks, some aftermarket companies offer torsion keys with different indexing positions, which provide added ground clearance and more adjustment than is offered with the stock pieces. Installation of the torsion keys is a minor project.
While raising a vehicle through increasing pressure on the torsion keys is a relatively simple adjustment, the practice can be dangerous. Raising the suspension by raising the torsion keys applies a tremendous load on several suspension components. Ball joints, tie rods, axles and constant velocity joints may fail prematurely. The torsion bar itself is more prone to fail and break due to the tremendous load placed upon it. The vehicle will also have a much rougher ride due to the limited travel of the suspension.
The torsion keys are adjusted by raising the vehicle and placing supports underneath the chassis. Located underneath the vehicle on the torsion bar, the keys are at the end that is furthest from the wheel. The adjusting bolt that runs through the key and rests against the vehicle's chassis is used to raise the vehicle by turning the bolt in as far as possible to gain maximum lift. The vehicle is lowered by turning the bolt out as far as possible; however, totally removing the adjustment bolt could cause damage to the key.
When making adjustments to any torsion bar suspension, it is wise for a user to record the number of turns made to each side of the vehicle. This assures the suspension can be returned to its original position and aids in setting each side to the same height. Due to differences and tolerances in manufacturing, it is possible that the two sides will require subtle to major differences in adjustment to attain the same results.